1. Field of the Invention
The present invention relates to an aromatic polycarbonate and the production method thereof. More particularly, it relates to an aromatic polycarbonate having less content of a low molecular weight oligomer, a narrow molecular weight distribution and an excellent heat resistance and the production method thereof.
2. Description of the Related Art
Heretofore, it has been known to produce an aromatic polycarbonate by the use of an aromatic dihydroxy compound, a carbonate precursor, an alkali metal or alkaline earth metal base, water, an organic solvent, a polycarbonate formation catalyst (often called a polymerization catalyst or a polycondensation catalyst) and an endcapping agent (often called a molecular weight modifier, a polymerization terminator or a chain stopper).
U.S. Pat. No. 3,275,601 discloses a method for preparing an aromatic polycarbonate by the use of bisphenol A as an aromatic dihydroxy compound, phosgene as a carbonate precursor, sodium hydroxide as an alkali metal base, dichloromethane as an organic solvent, triethylamine as a polycarbonate formation catalyst and p-tert-butylphenol as an endcapping agent. According to the method, an aromatic polycarbonate is prepared by introducing an endcapping agent into a reaction system before adding phosgene.
U.S. Pat. No. 3,974,126 discloses a method for continuously preparing a polycarbonate having an improved molecular weight distribution. The method comprises reacting a mixture of a chloroformate oligomer, a dihydroxy compound and an endcapping agent in a turbulent flow until the viscosity of the polycarbonate reaches 10-90% of the final viscosity of 300-4000 cps and further reacting the mixture in a laminar flow until the viscosity of polycarbonate reaches a final viscosity. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (a chloroformate oligomer).
Japanese Patent Application Laid-Open No. Sho 62-89,723 discloses a method for preparing a polycarbonate which comprises reacting an aqueous base solution containing an aromatic dihydroxy compound with phosgene in the presence of an organic solvent to form a low molecular weight polycarbonate and forming a high molecular weight polycarbonate in the reaction medium kept under emulsion conditions. According to the method, an endcapping agent is added before or immediately after introducing phosgene and the resulting low molecular weight polycarbonate is kept under emulsion conditions. Subsequently, when the concentration of the aromatic dihydroxy compound remaining in an aqueous phase shows the minimum, an endcapping agent is added again to carry out the polymerization resulting in forming a high molecular weight polycarbonate. The method is characterized in that before or immediately after introducing phosgene an endcapping agent is added to prepare an aromatic polycarbonate.
U.S. Pat. No. 4,737,573 discloses a method for preparing a linear polycarbonate. The method comprises (1) preparing a bischloroformate oligomer composition by passing phosgene into a mixture of water, an organic liquid and an aromatic dihydroxy compound, and simultaneously introducing an aqueous base solution at a rate to maintain the aqueous phase at a pH in the range of 8-11, (2) passing an endcapping agent and a polycarbonate formation catalyst into the mixture containing the compositions, and simultaneously introducing an aqueous base solution at a rate to maintain the aqueous phase of the mixture at a pH in the range of 11-12.5 to form a polycarbonate, and (3) recovering the linear polycarbonate to produce an aromatic polycarbonate. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (a bischloroformate oligomer composition).
U.S. Pat. No. 4,743,676 discloses a method for preparing linear aromatic polycarbonates of controlled molecular weight. The method comprises (A) reacting an aromatic bischloroformate composition with an endcapping agent in an essentially phosgene-free reaction system comprising water, an organic solvent and a base to produce a partially capped bischloroformate composition, and (B) contacting said partially capped bischloroformate composition with a polycarbonate formation catalyst and an aqueous base solution to form a linear aromatic polycarbonate. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (a bischloroformate composition).
U.S. Pat. No. 4,939,230 discloses a method for preparing a polycarbonate. The method comprises (A) forming a reaction mixture of an aromatic dihydroxy compound, a carbonate precursor, a solvent and a base, and (B) adding an endcapping agent to said mixture. In addition, the above-identified patent shows that the timing for adding an endcapping agent is when the reaction heat in the step A reaches a certain level. In other words, the addition of the endcapping agent is carried out immediately after introducing a carbonate precursor (cf. U.S. Pat. No. 4,722,995 ). Thus, according to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer.
U.S. Pat. No. 4,973,664 discloses a method for converting an aromatic bischloroformate composition to an aromatic polycarbonate having a predetermined weight-average molecular weight. The method comprises (A) partially capping said aromatic bischloroformate composition by the reaction with an endcapping agent in an amount to provide the desired molecular weight, and (B) contacting an organic solvent solution containing the partially capped bischloroformate composition with a polycarbonate formation catalyst, water and a base, the aqueous phase of the reaction mixture being buffered to maintain the pH thereof in the range of about 12-13. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (an aromatic bischloroformate composition).
U.S. Pat. No. 5,034,505 discloses a method for preparing an aromatic polycarbonate. The method comprises (A) contacting an aromatic bischloroformate composition and an endcapping agent in a single step under reaction-promoting conditions in a heterogeneous reaction medium comprising water and an organic solvent by introducing a polycarbonate formation catalyst and a base into the mixture of the aromatic bischloroformate composition and the endcapping agent, said base being introduced without pH control and an amount thereof being at least stoichiometrically sufficient to convert all of the bischloroformate to polycarbonate of the desired molecular weight and to finally form a non-emulsified heterogeneous system, and (B) continuing the addition of a base incrementally as necessary to bring the pH of the aqueous phase of the reaction mixture to a value within the range of about 10-13. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (an aromatic bischloroformate composition).
U.S. Pat. No. 5,043,203 discloses a method for preparing a polycarbonate using an endcapping agent of about 0.5-8 mole % based on one mole of aromatic dihydroxy compound. The method comprises (1) introducing phosgene into an agitated mixture comprising an aromatic dihydroxy compound at a temperature of about 15.degree.-50.degree. C. under interfacial reaction conditions and a pH between about 3-11.2, (2) continuing the phosgenation of the mixture and further introducing an aqueous base solution in accordance with a previously established set point between pH 3-10.5 comprising either of pH Control System A which adds an aqueous base solution at a rate sufficient to substantially maintain the mixture at the previously established pH set point, or a pH Control System B which adds an aqueous base solution at a rate sufficient to provide a ratio of moles of an aqueous base solution to moles of phosgene having a value of up to about 2.5, (3) allowing the introduction of an aqueous base solution to proceed in accordance with (2) until a sudden increase in base demand is noted with Control System A or a sudden decrease in pH of at least one unit is noted with respect to Control System B, (4) continuing the introduction of phosgene and an aqueous base solution in accordance with (3) until an additional 0.0025 to 0.09 mole of phosgene per mole of an aromatic dihydroxy compound is introduced, (5) discontinuing the introduction of phosgene and an aqueous base solution, while continuing to agitate the resulting mixture until the mixture is substantially free of phosgene, while the pH is maintained between about 4 to 8, ( 6) introducing an endcapping agent into the mixture and, after or with the addition of the endcapping agent, providing a proportion of from about 0.05 to 2 mole % of a tertiary organic amine per mole of an aromatic dihydroxy compound and a sufficient aqueous base solution to maintain the pH of the resulting mixture of between about 9 to 12, (7) proceeding the reaction of monochloroformate oligomer, and (8) recovering an aromatic polycarbonate from the reaction mixture. According to the method, an aromatic polycarbonate is prepared by adding an endcapping to a low molecular weight oligomer.
Japanese Pat. Laid-Open No. Hei 3-109420 discloses a method for continuously preparing a polycarbonate oligomer having a number-average molecular weight of 300-10000 by the reaction of an aqueous base solution containing an aromatic dihydroxy compound with phosgene in the presence of an organic solvent. The method comprises (1) supplying phosgene and an aqueous base solution containing an aromatic dihydroxy compound in tubular reactors pressurized to at least saturated vapor pressure of an organic solvent to conduct phosgenation reaction, an amount of the base being 0.9-1.5 equivalents based on the aromatic dihydroxy compound, and an amount of the aromatic dihydroxy compound being 0.55-0.95 mole based on the phosgene to effect phosgenation, (2) adding an endcapping agent at the inside of the tubular reactors or the outlets of the tubular reactors after the completion of the phosgenation reaction to conduct a partial termination reaction of the compound formed in (1) having chloroformate groups, (3) oligomerising the products in the next reactors until the reaction system has a pH of 5-10. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (a compound having chloroformate groups).
European Pat. Publication No. 502515 discloses a method for preparing a polycarbonate resin having an OH/CO ratio of 0.25 or less found from a ratio of absorbances of terminal OH and CO measured by an infrared spectrophotometer. The method comprises emulsifying after adding an endcapping agent to an oligomer-containing reaction mixture obtained by the reaction of an aqueous base solution of an aromatic dihydroxy compound with phosgene in the presence of an organic solvent, and polymerizing while the reaction mixture is allowed to stand still in the emulsified state. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (an oligomer).
U.S. Pat. No. 5,182,361 discloses a method for continuously preparing an aromatic polycarbonate having a high molecular weight by a boundary face condensation of a carbonate oligomer with a polycarbonate formation catalyst in the presence of an endcapping agent, a base, water and an organic solvent at a temperature of at most 70.degree. C. The method comprises mixing components in static mixers to form a fine dispersion, reacting the dispersion in a residence zone with plug flow, and repeating this combination of the steps at least once. According to the method, an aromatic polycarbonate is prepared by adding an endcapping agent to a low molecular weight oligomer (a carbonate oligomer).
However, even though any of the above-mentioned methods is used, the resulting aromatic polycarbonates have a large content of a low molecular weight oligomer and a molecular weight distribution thereof is broad.
On the other hand, U.S. Pat. No. 4,880,896 discloses an aromatic polycarbonate having less content of a low molecular weight oligomer. However, this aromatic polycarbonate is obtainable by treating the aromatic polycarbonate with a poor solvent such as acetone, methyl ethyl ketone and the like after isolating an aromatic polycarbonate prepared by a conventional method.
Recently, there has been desired a method for preparing an aromatic polycarbonate having less content of a low molecular weight oligomer and a narrow molecular weight distribution.